The field of the invention relates to air/fuel ratio control of engines having fuel vapor recovery systems.
For an engine having a fuel vapor recovery system coupled between a fuel system and engine air/fuel intake, feedback control systems are known which generate a feedback variable by integrating the output of an exhaust gas oxygen sensor. Liquid fuel injected into the engine is trimmed in response to the feedback variable in an attempt to maintain stoichiometric combustion.
A modification to this conventional system has been proposed wherein a second feedback system adaptively learns the inducted quantity of recovered fuel vapors. The difference between the feedback variable and a reference corresponding to stoichiometry is integrated to generate the learned value. Delivery of injected fuel is then reduced by the learned value to maintain stoichiometric combustion while purging fuel vapors from the fuel vapor recovery system. The inventor herein has recognized a problem with the proposed approach. When the engine is operating rich of stoichiometry because of factors other than vapor purging, such as deceleration, the rich offset may be erroneously learned as purged fuel vapor. An erroneous air/fuel correction may therefore be provided.